The present invention generally relates to an information recording medium where the data is recorded and reproduced in sectors of a given length, and an information recording and reproducing apparatus for recording and reproducing the data with the use of the information recording medium.
A ROM disk having previously recorded data on at least one portion of the information recording medium is being used at the object of distributing software and so on to many users with lower prices. The data format of the ROM disk is being standardized with 90 mm rewritable optical disks provided as the subject in the Optical Disk Standardization Committee (ISO/IEC JTC1/SC23/WG2). The contents thereof are described in the proposal: N72 10090.
FIG. 8 is an area layout showing schematically the layout of each area assigned to the partial ROM disk described in the draft proposal. In FIG. 8, a rewritable area where the data recording and reproducing may be performed and a ROM area where only data reproduction may be performed are assigned within the user area where the user data is recorded. In addition to the user area, a defect management area where the control data of the user area and the defect lists are recorded and a control track area where the disk control data of the optimum laser power and so on are recorded are assigned to specific locations on the disk. Although the management data is recorded on both the sides of the user area in the proposal in order to improve the reliability, a detailed description thereof has been omitted so as to simplify this description. The defect management area is composed of a primary defect list area for recording the primary defect list where the addresses of the defective sectors detected from the rewritable area in the format processing is stored during the format processing; a secondary defect list area for recording the secondary defect list where addresses of the defective sectors detected from the rewritable area and the address of the alternate sectors are collectively stored during the data recording operation; and, a disk definition area for recording the disk definition structure, where the management data of the respective areas assigned to the disk is recorded. The committee proposal defines a rewritable disk where the entire user area is a rewritable area and a ROM disk where the entire user area is a ROM area.
In the control track area and the ROM area, a concave-convex shaped track is formed at the disk manufacturing time so as to record the information. Although the data can be read from these areas, the recorded information cannot be rewritten. As the optical characteristics in these areas are different from the rewritable area, the data recording and reproducing apparatus is required to identify the ROM area for the focus control, the tracking control, the reproducing signal processing, and the write protection function with respect to the ROM area and so on. As the existence of the ROM area and the size thereof are different depending upon the disk, the start track address and the end address are recorded within the control track area as the management data of the ROM area.
FIG. 9 is an area layout of the ROM area interior formed within the user area. In FIG. 9, the ROM area is divided into a plurality of ROM groups. The ROM group is composed of data sectors with the user data being recorded on it, and parity sectors with the parity data being recorded on it. When one track is composed of 25 sectors, the most fundamental ROM group is composed of one track with the sector 0 through the sector 23 being assigned to the data sector and the sector 24 being assigned to the parity sector. At this time, the parity data to be recorded on the parity sector is defined as follows with the user data of the k the byte in the sector n being D (n,k). EQU D(24, k)=D(0,k) * D(1,k) *. . . * D(23,k)
where an operator * shows an exclusive OR operation. When, for example, the sector 0 has been detected as an uncorrectable error sector in the error correction processing, the user data of the error sector is computed from the following formula using correct data read from all the other sectors to be included in the ROM group. EQU D(0,k)=D(1,k) * D(2,k) *. . . * D(24,k)
FIG. 10 is a data block diagram of a disk definition structure for managing the respective areas assigned to the disk. A data identifier with (0A0A)h is recorded on the head for identifying that the read data is the disk definition structure. A certification flag following it is a flag showing whether or not the certification of the rewritable area has been performed during the format processing. Followed by them, the management data of the rewritable area and the ROM area assigned to the user area are recorded. The management data of ROM area includes number of the ROM groups, the number of data sectors per group and the number of parity sectors per group. Finally, the start addresses of the respective areas are recorded as the management data of the primary defect list area and the secondary defect list area.
But in the development process of such a ROM disk, the disk manufacturing step from the cutting process of the master disk having the ROM area to the disk duplication process using the stamper is carried out. Accordingly, when the manufacturing number of the ROM disks is as restricted in number as, for example, several hundred, the manufacturing cost per disk becomes higher. On the other hand, in the editing process of the application data, the sample ROM disk is made after the operation of the application has been confirmed on the magnetic disk drive unit. But in the operation test using the sample ROM disk, the reduction in the performance because of the difference in the data transfer speed between the magnetic disk drive unit and the optical disk drive unit or the inconvenient operation due to application bugs which rewrite the data on the magnetic disk may be detected. As several kinds of sample ROM disks are normally made before the operation test of the application is completely confirmed, the editing process of the ROM disk becomes longer.